In a liquid crystal projector, white source light is separated into beams of its three primary colors. Each beam is then infused with an image by a liquid crystal light valve or micro-LCD. Finally, the three beams are recombined into a single image and projected onto a display device (a screen).
The micro LCD's generate a representation of the image to be projected by using many small picture elements or pixels. Therefore, the above mentioned beams of light that emerge from the micro-LCD's are pixellated representations of the particular color components of the image. Thus, an accurate projected image requires that the pixels of the three infused beams be precisely aligned during the recombination step, meaning that the micro-LCD's themselves must be carefully positioned. In order to optimally orient the micro-LCD's the following requirements must be met.
(1) 6 degree of freedom (dof) adjustment capability must be available. Both rotation and linear translation with respect to three perpendicular axes are required in order to ensure that proper image alignment can be caused to occur.
(2) Adjustment mechanisms must have high resolution controls. Because of the small size of the pixels, direct manual adjustments are too crude to achieve proper alignment. Some sort of interface must be provided which can transform relatively large-scale operator inputs into micro-LCD motions of a magnitude commensurate with the pixel size.
(3) Adjustment mechanisms must provide positive positioning constraints. Since multiple operations are required to tune all 6 degrees of freedom, intermediate adjustments must have some amount of resistance to motion. Positioning devices typically have some sort of final locking mechanism, but to activate and deactivate that mechanism numerous times over the course of adjustment is cumbersome and often impossible. Therefore, any robust positioning device must provide for physical locating effects, rather than relying on balance, gravity or friction.
(4) The individual magnification of each image must be independently adjustable. There must be a means for making slight adjustments to the projected size of the image from any projection device. This means must be simple, inexpensive, and easy to use such that adjustments can be made quickly during the production process. Conventional positioning systems have either provided limited adjustment capability or else have use complicated mechanisms. For example, in U.S. Pat. No. 5,418,586 issued to Fujimori, a light valve positioning system is disclosed which uses a combination of plates, posts, and screws to provide the full 6 degree of freedom adjustment capability. However, while the mechanism taught by Fujimori provides a significant improvement in the field, it utilizes 6 major components and 14 adjustment screws. In addition, in spite of Fujimori's own listing of problems associated with eccentric pins (manufacturing difficulty, increased part count due to supporting components, non-linear relationship between rotational input and linear translation output, and the like), the mechanism of Fujimori still includes three such pins. Also, the mechanism of Fujimori utilizes a number of direct manual adjustments, making precise control difficult. For instance, a typical adjustment procedure used according to the Fujimori teachings is represented in the rotation of the liquid crystal valve about a vertical axis. This procedure involves rotating a flat head screwdriver in a slot formed by a notch in a light fixing plate and a hole in a lower adjustment plate. In this operation, the scales of the operator inputs are completely out of scale compared to the required adjustments, making proper alignment impossible. In addition, because the adjustment actuator (the flat head screwdriver) is removed once the desired rotation is achieved, the position of the light fixing plate is not positively secured, This allows motion to occur during the actual fixing process when the fixing screws are tightened, potentially causing misalignment of the liquid crystal light valve.
Many of these concerns have been addressed in a copending patent application Ser. No. 08/970,957 entitled MECHANICAL CONVERGENCE DEVICE FOR MICRO-LCD, which has an inventor in common with this present invention. The MECHANICAL CONVERGENCE DEVICE FOR MICRO-LCD provides all of the requirements discussed above and avoids the pitfalls. Indeed, for some applications the MECHANICAL CONVERGENCE DEVICE FOR MICRO-LCD may be superior to the present invention. However, the MECHANICAL CONVERGENCE DEVICE FOR MICRO-LCD is still quite complicated and is relatively expensive to manufacture.
It would be advantageous to have a device for positioning a micro LCD in a projection device so as to provide for optimal accuracy of adjustment and ruggedness, while maintaining optimal simplicity and economy. However, to the inventor's knowledge, no prior art method or means has achieved this combination of goals. Such devices have all been either to complicated and expensive and/or too difficult to adjust, or else have been overly delicate and/or expensive to produce.